Generally speaking, the power source of a central processing unit (CPU) in a computer system is not provided by a power supply directly. The main reason is that the core voltage (Vcore) needed by the CPU varies according to the value of a load. Since the core voltage (Vcore) may be increased or decreased instantaneously, the power supply cannot respond to the sudden change immediately. To solve the problem, a voltage regulator module (VRM) which specially provides power to the CPU is provided on the motherboard.
FIG. 1 is a schematic diagram showing a conventional single-phase VRM of a motherboard. The single-phase VRM 10 includes a pulse width modulate (PWM) control unit 102, a PWM driver 104, and an output unit 106. The PWM control unit 102 can output a PWM signal to the PWM driver 104.
Additionally, the PWM driver 104 includes a steering logic circuit 1042 and two driving circuits 1044 and 1046. The steering logic circuit 1042 generates a first signal and a second signal according to the PWM signal. The two driving circuits 1044 and 1046 generate a first driving signal S1 and a second driving signal S2 after receiving the first signal and the second signal, respectively.
Furthermore, the output unit 106 includes an upper power field effect transistor (FET) M1, a lower power FET M2, an output inductor L, a current sense resistor Rs, and an output capacitor Co. The drain electrode of the upper power FET M1 is connected to a power source voltage Vcc. The gate electrode of the upper power FET M1 receives the first driving signal S1. The source electrode of the upper power FET M1 is connected to a first end of the output inductor L. The drain electrode of the lower power FET M2 is connected to the first end of the output inductor L. The gate electrode of the lower power FET M2 receives the second driving signal S2. The source electrode of the lower power FET M2 is connected to ground (GND). The current sense resistor Rs is connected between a second end of the output inductor L and a core voltage output end Vcore. The output capacitor Co is connected to the core voltage output end Vcore and the GND.
Driven by the first driving signal S1 and the second driving signal S2, the output inductor L and the current sense resistor Rs generate output current Io to the core voltage output end Vcore. It can be known that whether the CPU operates at a heavy load or a light load according to the output current Io. When the CPU is detected to be at heavy load by detecting a sense voltage Vs across the current sense resistor Rs, the PWM control unit 102 may increase the pulse width of the PWM signal to increase the output current Io. Conversely, when the CPU is detected to be at light load by detecting a sense voltage Vs across the current sense resistor Rs, the PWM control unit 102 decreases the pulse width of the PWM signal to decrease the output current Io.
The more phases the VRM has, the more PWM drivers 104 and the output units 106 the VRM includes. Conventionally, a motherboard always uses the multi-phase VRM (multi-phase VRM). The multi-phase VRM can provide enough core voltages to a CPU when the CPU is at the heavy load.
FIG. 2 is a schematic diagram showing that a conventional four-phase VRM on a motherboard supplies power to a CPU. The four-phase VRM 20 includes a PWM control unit 202, four PWM drivers 204, 206, 208 and 210, and four output units 212, 214, 216 and 218.
The PWM control unit 202 can output four-phase pulse signals (PWM1 signal, PWM2 signal, PWM3 signal, PWM4 signal) to the PWM drivers 204, 206, 208 and 210, respectively. The output unit 212 cooperated with the PWM driver 204 outputs a core voltage Vcore-1 having a first phase. The output unit 214 cooperated with the PWM driver 206 outputs a core voltage Vcore-2 having a second phase. The output unit 216 cooperated with the PWM driver 208 outputs a core voltage Vcore-3 having a third phase. The output unit 218 cooperated with the PWM driver 210 outputs a core voltage Vcore-4 having a fourth phase. Consequently, the core voltage Vcore needed by a CPU 22 is provided by the four-phase VRM 20 according to the PWM1 signal, the PWM2 signal, the PWM3 signal, and the PWM4 signal. Since the circuits of the four PWM drivers 204, 206, 208, and 210 are the same as the circuit of the PWM driver 104 in FIG. 1, and the four output units 212, 214, 216, and 218 are the same as the circuit of the output unit 106 in FIG. 1, the operating principle thereof are not described for a concise purpose.
The stability of the CPU is improved along with the increase of the number of phases of the VRM, but companies have to consider the efficiency of the VRM. The more phases the VRM has, the more energy are consumed. Furthermore, there is a problem that the efficiency of the VRM is low at the light load. The CPU 22 transmits a power state indicator (PSI) signal when the CPU 22 operates at a load lower than the lowest load, and the motherboard requires the four-phase VRM 20 to only enable a single phase to supply power to the CPU 22. For example, Only the core voltage Vcore-1 having the first phase outputted by the output unit 212 cooperating with the PWM driver 204 supplies power to the CPU 22 to realize the optimization of the efficiency of the VRM. However, conventional VRMs can only switch between the four-phase power supply and the single-phase power supply (taking the four phase VRM as an example). People focus on energy saving today, and it wastes energy.